The App Revolution

Another way that the iPad is like the iPhone and iPod Touch is with the proliferation of specialty apps. Many of the developers who have already created iPhone apps have modified those apps into HD versions that take full use of the larger screen of the iPad. Virtually every app designed for the iPhone is also compatible with the iPad. On an iPad, the iPhone apps can be viewed in either small (1X) format, exactly the same size as the iPhone's display, or in a full screen (2X) zoom format that does exhibit some pixilation due to the expanded view.

This is a significant change. You might recall that apps were not a part of the original iPhone experience. The ecosystem of apps evolved outside of official channels and there was initially a lot of tension between the app developers and Apple, until the latter decided to officially sanction the concept by creating developer tools and opening the App Store.